I've started saving paintings (etc) of trees in a file. Drawing or painting a representational or even photorealistic version of a tree is not the easiest thing in the world, but drawing or painting a conceptual tree, or abstracted tree, or windblown tree and its movement, oy vey.
I know an artist who does complicated ink drawings of nature with dots. It takes her hundreds of hours per drawing. In that case, any given dot hasn't the importance of, say, one beautiful line. I can slightly understand it since before I ever took a drawing class I tried to do a copy of a two page ink drawing of vegetables in the los angeles times magazine - with a quill pen that kept catching wee bits of the paper I was using and needed to be wiped off at every single use of the pen. Talk about nuts, but it was engrossing at the time. Never did that
Best way to learn to draw or paint trees.. look at them, again and again, for form and gesture of the tree, look at the details, then forget the details except the important ones (which important ones?, well, that's part of the decision making, or play). Trees have 'personalities', or represent something, or have a certain posture, or...
some trees are tortured, or tortuous. Some streak for the sky..
anyway, have fun.